In engine design there may be trade-offs between strength, weight, and other properties of materials used to construct the cylinder head and block. For example, cast iron has been used to manufacture cylinder blocks. Cast iron may have several benefits over other materials, such as a smaller volume to strength ratio and a smaller friction coefficient, decreasing the engine's size and increasing combustion chamber longevity. However, cast iron cylinder blocks may have a low strength to weight ratio, may be more susceptible to corrosion, and may have undesirable heat transfer characteristics. In order to reduce block weight and increase the amount of heat transferred to water jackets, cylinder blocks may be cast out of aluminum.
A reduction in block weight may also be obtained by using an engine block made from a fiber-reinforced phenolic resin as shown by Holtzberg in U.S. Pat. No. 4,848,292. In this example, the phenolic resin, as a matrix, is reinforced by fiberglass or graphite fibers. The engine block may be produced either by injection molding or compression molding.
The inventors herein have identified potential issues with the approach of Holtzberg. For example, injection molding of fiber reinforced composite material to form engine blocks may result in non-uniform distribution of the reinforcing fibers. As an example, the reinforcing fibers may be unevenly distributed along critical load pathways of the engine block. In another example, the composite material by itself may not possess desired mechanical properties particularly along pathways encountering dynamic loads, structural loads, thermal loads, and loads from attachment to external devices.
The inventors herein have recognized the above issues and developed an approach to at least partly address the above issues. In one example approach, a method for molding an engine block is provided, comprising reinforcing the engine block with a plurality of metal strips, wherein a first portion of the plurality of metal strips are positioned in a substantially transverse direction of the engine block and a second portion of the plurality of metal strips are positioned in a substantially longitudinal direction of the engine block. In this way, additional reinforcement may be provided along specific pathways that may experience higher loads while simultaneously reducing engine weight.
For example, an engine block may be formed from a thermoset composite material via a molding process such as injection molding. In one example, the composite material may include a thermoset polymer matrix reinforced by glass, carbon, and/or aramid fibers. Prior to commencing the molding process, a plurality of additional metal reinforcement strips may be positioned in predetermined locations within a mold of the engine block. The strips may be manufactured from metals such as titanium, titanium alloys, or similar materials that possess a higher specific strength. Further, the predetermined locations may be in substantially longitudinal directions along the engine block and/or in substantially transverse directions of the engine block. In addition, reinforcement strips may be located along a substantially vertical direction of the engine block. As an example, the predetermined locations may include pan rails in a longitudinal direction of the engine block, a head deck in a transverse direction of the engine block, head bolt columns in a vertical direction of the engine block, and other similar regions that may experience higher loads. During injection molding, the composite material may fill spaces around the reinforcing strips and encapsulate the reinforcing strips within the formed structure of the engine block. The reinforcing strips may, thus, be integrally molded into the cylinder block at desired locations. As such, the reinforcement strips may be distinct from the reinforcing fibers distributed within the thermoset polymer matrix. It will also be noted that the reinforcing strips may be formed from a different material than the composite material used for the engine block.
In this way, a cylinder block of a lightweight composite material may be further reinforced to provide desired mechanical properties. Reinforcing strips may be positioned along paths within a mold for the cylinder block that may be exposed to substantial dynamic loads, thermal loads, or structural loads. Thus, specific locations within the cylinder block may be strengthened for improved performance and structural stability. By incorporating additional reinforcements where desired, adverse effects of non-uniform distributions of the fiber fill in the polymer matrix during molding may be reduced. Overall, structural properties of the cylinder block may be improved while maintaining a lower engine block weight.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Additionally, the above issues have been recognized by the inventors herein, and are not admitted to be known.